HMG-CoA reductase has been shown to be the major regulatory enzyme in hepatic cholesterol biosynthesis. In view of the probable relationship between elevated levels of plasma cholesterol and atherosclerosis, an understanding of the regulation of cholesterol biosynthesis by this enzyme is of medical importance. We have developed techniques which allow for the first time preparation of purified HMG-CoA reductase possessing a high specific activity (14- to 66-fold higher than previously achieved in other laboratories). The key to this procedure is development in our laboratory of an affinity chromatography procedure for HMG-CoA reductase purification. This purification procedure will give us an excellent opportunity to define the mechanisms for enzyme inactivation by various natural inhibitors. In addition, a major objective of this project is the chemical synthesis of inhibitors of HMG-CoA reductase which hopefully would possess the ability to regulate the rate of cholesterol synthesis in vivo.